Melt direct spinning-prepared high and low viscosity pet bicomponent elastic fiber and preparation method therefor

Abstract

The present invention relates to a melt direct spinning-prepared high and low viscosity PET bicomponent elastic fiber and a preparation method therefor. The preparation method utilizes a six vessel procedure. In addition to using terephthalic acid and ethylene glycol to carry out first and second esterification reactions and first and second pre-polymerization reactions, the resulting polyethylene terephthalate prepolymer is respectively introduced into a high viscosity final polymerization vessel and a low viscosity final polymerization vessel to undergo polymerization; high viscosity and low viscosity PET melts are separately obtained, which are then spun together. During the preparation process, heat stabilizers, antioxidants, coloring agents, solid phase slip agents, viscosity reducers, and liquid phase lubricants may be added. Utilizing this method, the viscosity of the high viscosity component is significantly increased, and a wider range of viscosity differences between high and low viscosity polyester melts is obtained. The difference in intrinsic viscosity between high and low viscosity melts is controlled within 0.100-0.550; and a prepared PET / PET bicomponent elastic fiber is high quality and has excellent crimp contraction.

Description

A melt-spun high- and low-viscosity PET bicomponent elastic fiber and its preparation method Technical Field

[0001] The invention relates to a melt-spun high- and low-viscosity PET bicomponent elastic fiber and a preparation method thereof. Background Art

[0002] The application scope of elastic fibers in the modern chemical fiber industry is becoming wider and wider. Especially in recent years, with the rapid development of the theory of bicomponent elastic fibers, we have a deeper understanding of the forming mechanism and elasticity generation mechanism of parallel bicomponent elastic fibers, and the varieties of elastic fibers and original technologies have also made great progress. Starting in the 1970s, DuPont first launched single-component spandex elastic fiber, which quickly became popular in the market for its unique style and characteristics. In the late 1970s, it launched the two-component parallel elastic fiber T800, which uses PBT / PET parallel composite to produce good elastic effect. However, due to the low glass transition temperature (26-42°C) of the PBT component of PBT / PET elastic fiber, the fiber undergoes rapid crystallization under stress, and the elastic recovery rate and shape retention of T800 fiber are poor. In the 21st century, with the successful industrialization of PDO by chemical and biological fermentation methods, PTT polyester has a unique molecular structure and excellent elastic recovery properties. DuPont's T400, PTT / PET two-component elastic fiber, was launched. The PTT / PET two-component parallel composite fiber has excellent elastic recovery rate and shape retention. The fabric will not deform after repeated stretching. Its elastic sustained-release effect overcomes the restraining feeling of spandex elastic fiber. With its excellent resistance to chlorine bleaching and light exposure, it has become the best elastic fiber variety in the fabric industry.

[0003] However, the price of PTT polyester raw materials is high, and PTT / PET two-component fibers are basically used in the category of high-end fabrics. For some fabrics with lower elasticity requirements, the cost-effectiveness is not outstanding. Therefore, the development of two-component elastic fibers has become a key area of ​​development in the industry in the past decade. The latest progress is to utilize the different orientation and crystallization behaviors between different viscosity components of PET polyester, and use high-viscosity PET and low-viscosity PET with a certain viscosity difference for parallel spinning to prepare PET / PET two-component elastic fibers. During the spinning process, the high-viscosity component and the low-viscosity component produce elastic curling due to the different speeds and percentages of transition from the orientation state to the crystallization state, forming a spring-like structure, thus showing a good elastic effect on the fabric. Patents such as CN111101237A, CN101126180A, CN106337212A, CN107964690A, CN101851812A, and CN115613159A respectively disclose a series of methods for preparing parallel composite elastic fibers such as PET / PET, PBT / PET, and PTT / PET, as well as methods for preparing easily dyed or deeply dyed elastic fibers by using modified PET with elasticity retention, such as high-viscosity ECDP, high-viscosity high-shrinkage polyester, high-viscosity disperse dye-easy polyester, high-viscosity CDP cationic polyester, etc., and low-viscosity PET polyester.

[0004] The preparation methods of the above-mentioned elastic fibers are all based on a slice spinning production process in which high-viscosity slices and low-viscosity slices are pre-crystallized and melted by a drying screw, and then formed into a composite spinning box and a composite parallel spinneret. Although the basic parallel composite spinning technology problems have been solved, the slice spinning technology has obvious defects such as long process, high cost, low production capacity, and poor product quality stability.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a melt-spun high- and low-viscosity PET two-component elastic fiber, which can achieve very high elastic curl and can adjust different degrees of elastic curl, and has a low production cost. When preparing the elastic fiber, the viscosity of the high-viscosity melt is sufficiently high, and the high-viscosity melt can better maintain high viscosity during the melt conveying process, and the preparation method has high production capacity.

[0007] Another object of the present invention is to provide a method for preparing high-viscosity and low-viscosity PET bicomponent elastic fibers by melt direct spinning. The preparation method adopts a unique six-kettle polymerization device system to separately polymerize a high-viscosity melt component and a low-viscosity melt component, and then directly carries out parallel composite spinning of the two-component melts. High-viscosity and low-viscosity PET bicomponent elastic fibers can be prepared simply, significantly reducing production costs and improving production efficiency.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a PET bicomponent elastic fiber comprises the steps of sequentially subjecting terephthalic acid, ethylene glycol, and a catalyst to an esterification reaction in a first esterification kettle and a second esterification kettle, and then to a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain an ethylene terephthalate prepolymer. The method further comprises the steps of conveying the ethylene terephthalate prepolymer to a high-viscosity final polymerization kettle and a low-viscosity final polymerization kettle via separate melt pumps for polymerization reaction to obtain a high-viscosity PET melt and a low-viscosity PET melt, respectively, wherein the viscosity of the high-viscosity PET melt is greater than that of the low-viscosity PET melt; and spinning the high-viscosity PET melt and the low-viscosity PET melt through the same parallel composite spinning assembly to obtain the PET bicomponent elastic fiber. The difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.100 to 0.550.

[0010] In some embodiments, the PET bicomponent elastic fiber contains, by mass percentage, 30%-70% of a first PET component and 70%-30% of a second PET component, and the first PET component and the second PET component have different viscosities.

[0011] In the present invention, a six-reactor polymerization device system is used for polymerization, which can orderly adjust the viscosity difference between high-viscosity and low-viscosity melts (0.100-0.550), and then produce elastic fibers with different curl shrinkage rates according to the needs of different customers, greatly increasing the index range of the device products and the flexibility level of the device.

[0012] The PET bicomponent elastic fiber of the present invention contains a high-viscosity and a low-viscosity bicomponent. The preparation method of the aforementioned PET bicomponent elastic fiber is a melt direct spinning method, that is, the melt obtained by polymerization is directly used for spinning without the melt cooling and slicing step and then melting and spinning.

[0013] In some embodiments, the high-viscosity final polymerization kettle is a horizontal polymerization kettle and includes a main body containing a chamber therein. The main body includes a low-viscosity zone, a medium-high-viscosity zone, and a high-viscosity zone arranged in sequence along the axial direction of the high-viscosity final polymerization kettle. The viscosity of the polyethylene terephthalate melt in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increases in sequence. The length of the low-viscosity zone is three-fifths of the length of the high-viscosity final polymerization kettle, and the lengths of the medium-high-viscosity zone and the high-viscosity zone are two-fifths of the length of the final polymerization kettle. The high-viscosity final polymerization kettle also includes two stirring shafts, one of which is arranged in the low-viscosity zone and the other is arranged in the medium-high-viscosity zone and the high-viscosity zone. The central axes of the two stirring shafts are located on the same straight line. The length of the stirring shaft arranged in the low-viscosity zone is three-fifths of the length of the high-viscosity final polymerization kettle, and the length of the stirring shaft arranged in the medium-high-viscosity zone and the high-viscosity zone is two-fifths of the length of the high-viscosity final polymerization kettle. The high-viscosity final polymerization kettle also includes a trumpet-shaped high-viscosity melt outlet arranged at the rear end of the high-viscosity zone. This design is a dual-shaft stirring design with unequal front and rear ends.

[0014] In the present invention, three-fifths and two-fifths are not the exact mathematical values ​​of three-fifths and two-fifths, but refer to approximately three-fifths, two-fifths and thereabouts, and are approximately equal to three-fifths and two-fifths.

[0015] In some embodiments, multiple disc reactors are provided on both stirring shafts. The disc reactors in the low-viscosity zone are designed as a multi-disc group of 3 to 10 discs, the front end of the low-viscosity zone is designed as a multi-disc group of 10 to 6 discs, and the rear end of the low-viscosity zone is designed as a multi-disc group of 5 to 3 discs, resulting in 35 to 55 disc reactors in the low-viscosity zone. The high-viscosity final polymerization reactor also includes two circular distribution discs at the front end of the low-viscosity zone, each with six spokes, dividing the distribution disc into six equal parts. Sieve plates are provided in the three equally spaced sector-shaped areas, each with a large number of circular holes with a diameter of 1 to 5 cm. The distribution plates can control the material to prevent short-circuiting of low-viscosity materials, thereby making the molecular weight distribution of the melt more uniform.

[0016] In the present invention, the multi-disc group design refers to a plurality of adjacent disc reactors fixedly connected together, which are installed together with the stirring shaft. The 10-6 disc multi-disc group design refers to a plurality of 10-6 disc reactors fixed together.

[0017] In some embodiments, the disc reactor in the medium and high viscosity zone is designed with 4 combined discs, 3 combined discs and 2 combined discs from front to back; the medium and high viscosity zone is also provided with a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle; the disc reactor in the medium and high viscosity zone is 15 to 25 discs; the disc reactor in the high viscosity zone is designed with 2 combined discs, and the high viscosity zone is provided with 5 to 8 groups of 2 combined discs; the total number of disc reactors in the medium and high viscosity zone and the high viscosity zone is 25 to 35; the high viscosity zone is also provided with a composite scraper, and the composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle and a disc scraper for scraping the melt on the stirrer; in the 2-piece combined disc design of the high viscosity zone, the distance between the combined disc groups and the two discs themselves gradually increases from front to back. The double-disc design is suitable for the preparation of relatively low high-viscosity melts (too high viscosity will cause climbing pole effect), with high film-drawing and devolatilization efficiency, low construction difficulty, excellent product quality, effective reduction of residence time, and low degree of side reactions.

[0018] In the prior art, although scrapers are provided in conventional polymerization reactors, the scraper structure is relatively simple and its function is relatively limited. In the high viscosity zone of the high viscosity final polymerization reactor of the present invention, by adopting the composite scraper with the above-mentioned specific structure, the material renewal rate of the disc reactor, the stirring shaft surface and the wall surface of the polymerization reactor can be effectively controlled, so that the material in the three places will not accumulate too much, effectively suppressing the problems of hue degradation and large amounts of acetaldehyde generated during the production of high viscosity melt. The disc scraper portion of the composite scraper of the present invention can control the thickness of the disc melt film, the wall scraper portion can timely update the material on the wall of the polymerization reactor, and the axial scraper portion can clean the stirring shaft. By adopting the final polymerization reactor containing the above-mentioned composite scraper, the material residence time can be controlled to 75 to 120 minutes, which is much lower than the residence time of the conventional front and rear double-axis high viscosity disc reactor, which is usually around 180 to 300 minutes. The significant reduction in residence time effectively reduces the level of side reactions, which is beneficial to the preparation of high viscosity polyester melt.

[0019] In some embodiments, the intrinsic viscosity of the polyethylene terephthalate melt in the low-viscosity region is 0.45-0.60, and the dynamic viscosity is 90-240 Pa.s; the intrinsic viscosity of the polyethylene terephthalate melt in the high-viscosity region is 0.68-0.90, and the dynamic viscosity is 500-1000 Pa.s.

[0020] The high-viscosity melt in the high-viscosity final reactor has a very high dynamic viscosity. Under high dynamic viscosity conditions, the flow state of this non-Newtonian high-viscosity melt on the rotating disk of the disc reactor is significantly different from that of conventional, lower-viscosity polyester melts. The melt film thickness on the disc reactor increases sharply with increasing dynamic viscosity, which in turn causes a melt climbing effect, significantly extending the melt's residence time on the disc and significantly reducing the disc's mass transfer efficiency. In addition, under vacuum conditions, the volatilization and devolatilization efficiency of the ethylene glycol produced by the polycondensation reaction is significantly reduced, the system devolatilization rate is slow, and the axial material flow rate of the disc reactor is slow, significantly reducing the vertical and axial mass transfer and heat transfer efficiency. At extreme high dynamic viscosity, uninterrupted melt can flood the top of the disc reactor, resulting in blocked vacuum channels in the high-viscosity final reactor and affecting the polymerization process. Finally, the polymer material contacts the wall of the final polymerization kettle, making replacement difficult, causing the melt to stay on the disc reactor and the kettle wall for too long, greatly increasing the level of condensation side reactions. On the one hand, it greatly increases the amount of low-molecular by-products such as acetaldehyde in the final polymerization kettle. In severe cases, it may cause the vacuum system to be unable to devolatilize in time, resulting in a decrease in vacuum capacity. On the other hand, the materials that have been aggregated for a long time undergo catalytic cracking and cross-linking solidification, forming gel and carbonization, and forming a large number of gel particles and condensed particles, which seriously affect the end and full roll rate level of the product spinning process.

[0021] To this end, the present invention adopts a six-reactor polymerization device system consisting of a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, a high-viscosity final polymerization reactor, and a low-viscosity final polymerization reactor. The high-viscosity final polymerization reactor adopts two different designs, one of which is the aforementioned unequal length front and rear end double-shaft stirring design (the front chamber stirring shaft is three-fifths of the reactor length, and the rear chamber stirring shaft is two-fifths of the reactor length, wherein the front chamber is the low viscosity zone, and the rear chamber is the medium-high viscosity zone and the high viscosity zone). The high viscosity zone adopts a reinforced double-disc group design with a composite scraper, which is characterized by simple design and easy use, and is suitable for the production of medium- and high-viscosity polyesters. The other is the following design with equal length front and rear shafts, and the high viscosity zone of the rear chamber adopts a high-strength and high-efficiency single-disc design, and is used in conjunction with a composite scraper to more efficiently control the disc film formation. Since the material renewal efficiency in the high viscosity zone is higher and the degree of side reactions is effectively controlled, it is suitable for the production of higher viscosity melts.

[0022] In some embodiments, the high-viscosity final polymerization kettle is a horizontal polymerization kettle and includes a main body containing a chamber therein, the main body including a low-viscosity zone, a medium-high-viscosity zone, and a high-viscosity zone arranged in sequence along the axial direction of the high-viscosity final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increasing in sequence, the length of the low-viscosity zone is half the length of the high-viscosity final polymerization kettle, the length of the medium-high-viscosity zone and the high-viscosity zone is half the length of the high-viscosity final polymerization kettle, the high-viscosity final polymerization kettle further includes two stirring shafts, one stirring shaft is arranged in the low-viscosity zone, and the other stirring shaft is arranged in the medium-high-viscosity zone and the high-viscosity zone, the central axes of the two stirring shafts are located on the same straight line, the length of the stirring shaft arranged in the low-viscosity zone is half the length of the high-viscosity final polymerization kettle, and the length of the stirring shaft arranged in the medium-high-viscosity zone and the high-viscosity zone is half the length of the high-viscosity final polymerization kettle; the high-viscosity final polymerization kettle further includes a trumpet-shaped high-viscosity melt outlet arranged at the rear end of the high-viscosity zone. This design is a design with equal lengths of the front and rear shafts.

[0023] In the present invention, half does not refer to the exact mathematical value of half, but refers to a value approximately at or around half, and is approximately equal to half.

[0024] In some embodiments, multiple disc reactors are provided on both stirring shafts; the disc reactor in the low viscosity zone is designed as a multi-group multi-disc; the high viscosity final polymerization kettle also includes two circular distribution plates arranged at the front end of the low viscosity zone, each distribution plate having six spokes, which divide the distribution plate into six equal parts, wherein sieve plates are arranged in three equally divided fan-shaped areas at intervals, and each sieve plate is distributed with a large number of circular holes with a diameter of 1-5 cm.

[0025] In some embodiments, the disc reactor in the medium and high viscosity zone is designed with 8 to 10 groups of double discs; the disc reactor in the high viscosity zone is designed with a single disc, and the disc reactor in the high viscosity zone is 6 to 15 discs; the disc reactor in the high viscosity zone adopts a reinforced design; the high viscosity zone is also provided with a composite scraper, and the composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle, and a disc scraper for scraping the melt on the stirrer, the wall scraper is a spiral that rotates along the axial direction, the axial scraper and the disc scraper are arranged between the disc reactors, and the wall scraper is arranged at the outer edge of the disc reactor, and from front to back, the distance between the disc scraper and the adjacent disc reactor, and the distance between the wall scraper and the inner wall of the high viscosity final polymerization kettle gradually decreases; the diameter of the disc reactor in the high viscosity zone decreases from front to back, and the diameter of the last disc reactor in the high viscosity zone is 85% of the diameter of the first disc reactor. As the viscosity of the resulting polyester melt increases from the low-viscosity zone, through the medium-high viscosity zone, to the high-viscosity zone, the spacing between the disc reactors gradually increases. This prevents melt blockage and facilitates further propulsion and polymerization of the melt. This disc reactor design is based on the gradual increase in axial viscosity of the melt. The disc reactor radius gradually narrows, reducing the load on the agitator shaft while also gradually reducing the outer diameter of the rear disc reactor, increasing the area for volatiles to flow.

[0026] In the prior art, although scrapers are provided in conventional polymerization kettles, the scraper structure is relatively simple and its role is relatively limited. In the high viscosity zone of the high viscosity final polymerization kettle of the present invention, by adopting the composite scraper of the above-mentioned specific structure, the material renewal rate of the disc surface of the disc reactor, the surface of the stirring shaft and the wall of the polymerization kettle can be effectively controlled, so that the material in the three places will not accumulate too much, and the problems of hue degradation and large amounts of acetaldehyde generated during the production of high viscosity melt can be effectively suppressed. The disc scraper portion of the composite scraper of the present invention can control the thickness of the disc melt film, the wall scraper portion can timely update the material on the wall of the polymerization kettle, and the axial scraper portion can clean the stirring shaft. By adopting a final polymerization kettle containing the above-mentioned composite scraper, the material residence time can be controlled at 75 to 120 minutes, which is much lower than the residence time of the conventional front and rear double-axis high viscosity disc reactor, which is usually around 180 to 300 minutes. The significant reduction in residence time effectively reduces the level of side reactions, which is beneficial to the preparation of high viscosity polyester melt.

[0027] In some embodiments, the intrinsic viscosity of the polyethylene terephthalate melt in the low viscosity region is 0.45-0.60, and the dynamic viscosity is 90-240 Pa.s; the intrinsic viscosity of the polyethylene terephthalate melt in the high viscosity region is 0.68-0.90, and the dynamic viscosity is 450-1000 Pa.s.

[0028] For the above two stirring shaft designs, the following further structures or method steps can be adopted.

[0029] In some embodiments, the high-viscosity final polymerization kettle further comprises steam feed ports disposed at the top of the main body at the rear end of the low-viscosity zone, the rear end of the medium-high viscosity zone, and the rear end of the high-viscosity zone for introducing superheated ethylene glycol steam. The preparation method further comprises the step of metering the superheated ethylene glycol steam using a metering system and introducing the superheated ethylene glycol steam into the high-viscosity final polymerization kettle. Providing the above-mentioned steam feed ports in the final polymerization kettle allows for regular alcoholysis of the gel and carbonized materials produced in the high-viscosity zone during the long-term operation of the device, thereby preventing carbonization at the top of the reactor. Furthermore, the high-viscosity zone discs can be de-vised and removed in a timely manner based on the pressure increase of the spinning assembly, thereby depolymerizing and removing long-term aged and deteriorated materials from the disc surface, re-establishing the material distribution on the discs, and extending the device's operating cycle.

[0030] In some embodiments, the high-viscosity final polymerization kettle is connected to a vacuum pump, which is a liquid ring pump and a chilled water device for cooling the gas is provided at its inlet. The preparation method controls the suction volume of the vacuum pump to 200-350 kg / h, the ultimate vacuum degree of the vacuum pump to 50-65 Pa, and the vacuum degree in the final polymerization kettle is controlled to 100-180 Pa under the production state.

[0031] In the present invention, due to the increase in side reactions of materials in the high-viscosity zone and the overall decrease in the efficiency of devolatilization, the amount of volatile matter produced in the final polymerization kettle is 2.5 to 3.2 times that of a conventional polyester device with the same production capacity. The higher the viscosity of the high-viscosity outlet, the higher the amount of non-condensable gas produced. Therefore, the vacuum pump exhaust design is 2.0 to 3.0 times that of a conventional polyester device with the same production capacity, the ultimate vacuum design is: 50 to 65 Pa, the exhaust volume is: 200 to 350 kg / h, and a large-capacity chilled water device is designed at the inlet of the vacuum pump liquid ring pump to capture excess non-condensable acetaldehyde. In order to further maintain production stability, all ethylene glycol produced in the vacuum part of the device must be subjected to formaldehyde removal treatment before entering the system.

[0032] In some embodiments, the catalyst is a supported catalyst and includes a carrier and an active component; the carrier is nano-barium sulfate, the particle size of the nano-barium sulfate is 20 to 50 nm, and the specific surface area is 270 to 350 m 2 / g; the nano barium sulfate is prepared by reaction in anhydrous ethylene glycol; the active component includes a main active component and a secondary active component, the main active component is titanium oxide, and the secondary active component is a mixture of scandium oxide, magnesium oxide, cobalt oxide and zinc oxide.

[0033] In some embodiments, the catalyst contains 3.3% to 10.0% titanium oxide, 8% to 15% of secondary active components, and 75.0% to 88.7% of nano-barium sulfate, based on weight percentage.

[0034] In some embodiments, the particle size of the catalyst is 80 to 160 nm.

[0035] In some embodiments, the catalyst is prepared by precipitating an ethylene glycol suspension of a carrier, scandium sulfate, magnesium sulfate, cobalt sulfate, zinc sulfate, a titanium compound, and a precipitant, treating the surface with a silane coupling agent, and calcining.

[0036] In some embodiments, the scandium sulfate, magnesium sulfate, cobalt sulfate, and zinc sulfate are added in the form of aqueous solutions.

[0037] In some embodiments, the titanium compound is selected from tetrabutyl titanate (TBT) or tetraisopropyl titanate (TPT).

[0038] In some embodiments, the precipitant is sodium hydroxide, preferably a solution of sodium hydroxide in ethylene glycol.

[0039] In the present invention, a high-stability polyester formula is used, and PTA and EG are used for esterification and polymerization. The catalyst used is a self-developed titanium-based solid-phase multi-metal catalyst. When synthesizing the catalyst, nano-scale barium sulfate is first prepared in an ethylene glycol liquid phase, and the particle size of the barium sulfate is controlled to be 20-50 nm, and the specific surface area reaches 270-350 m 2 / g, and then controlling the pH value of the barium sulfate suspension at 7.0-7.1. Then, under high-speed stirring conditions, a scandium-magnesium-cobalt-zinc sulfate aqueous solution and a sodium hydroxide ethylene glycol solution are simultaneously added dropwise. The suspension is then aged, and a titanium compound is added dropwise. After further aging, a silane coupling agent is added dropwise to seal the powder surface. After further aging for 10.0 hours, water and low-boiling alcohol are distilled off, and the pH value is adjusted to neutral. The catalyst is then filtered and calcined to obtain the catalyst.

[0040] This titanium-based solid-phase multi-metal catalyst is porous and has a large specific surface area. It exhibits excellent dispersion in ethylene glycol, overcoming the hydrolysis vulnerability of conventional liquid-phase titanium catalysts during esterification polymerization. It offers superior catalytic performance and effectively suppresses side reactions. Compared to traditional antimony-based catalysts, this catalyst achieves improved thermal and thermo-oxidative stability of high-viscosity melts, reducing melt viscosity by approximately 12% to 18% compared to antimony-based catalysts.

[0041] In some embodiments, a melt pump is used to transport high-viscosity PET melt and low-viscosity PET melt, a melt cooler is provided at the outlet of the melt pump, and the preparation method controls the temperature of the high-viscosity PET melt to 284-286°C after cooling by the melt cooler; a filter and a booster pump are provided between the melt pump and the parallel composite spinning assembly; the preparation method controls the transport time of the high-viscosity PET melt to 25-35 minutes; and a plurality of static slow-flow mixers are provided at the front end of the melt transport pipeline.

[0042] In the present invention, an ultra-short process high-viscosity polyester melt efficient melt conveying design is designed; a large-capacity melt cooler is equipped at the outlet of each melt pump to ensure that the melt temperature is quickly controlled at: 284-286°C, and then the melt is conveyed to the spinning unit through a filter and a booster pump. The ultra-short process design concept is to transfer the final polymerization kettle from the polymerization device to the top of the spinning device, and the melt is delivered to the spinning unit with the shortest conveying time. The conventional polyester melt conveying time is generally 50-70 minutes, and the high-viscosity melt conveying short process requires the conveying time to be compressed to: 25-35 minutes. A more stringent design is that the residual internal stress kinetic energy of the melt must be completely released within this residence time range. Therefore, a special front-end multi-position static slow-flow mixer is designed to quickly achieve a plug flow effect without increasing the residence time.

[0043] In some embodiments, the preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PET melt before the high-viscosity PET melt passes through the filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, atmospheric pressure boiling-dyeable polyester EDDP, polybutylene terephthalate PBT, and polypropylene terephthalate-1,3-propanediol ester PTT.

[0044] Furthermore, the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt, preferably 0.5 to 2.0%, and more preferably 0.8 to 1.5%. Adding the viscosity reducer can significantly reduce the kinematic viscosity of the high-viscosity melt, improve the melt conveying efficiency, and reduce process degradation.

[0045] An additive injection system is designed in front of the high-viscosity melt conveying filter to inject the viscosity reducer. The addition of the viscosity reducer can greatly improve the fluidity of the high-viscosity melt, improve the internal stress elimination effect of the high-viscosity melt, and enhance the plug flow effect. It can achieve a more stable spinning effect and an improved fiber curvature without affecting the basic indicators and quality of the final two-component elastic fiber product.

[0046] In some embodiments, the preparation method further includes the step of passing a solid-phase smoothing agent into the ethylene terephthalate prepolymer before passing the ethylene terephthalate prepolymer into the high-viscosity final polymerization kettle, and the step of passing the mixture of the solid-phase smoothing agent and the ethylene terephthalate prepolymer through a filter, wherein the solid-phase smoothing agent is in the form of a masterbatch and includes a polyester matrix and an inorganic powder, and the inorganic powder is selected from a combination of one or more of talc, montmorillonite, barium sulfate, hydrotalcite and nano-silica.

[0047] Furthermore, the amount of the solid phase smoothing agent is 0.05% to 1.0% of the total mass of the melt, preferably 0.06 to 0.8%, and more preferably 0.1 to 0.5%.

[0048] Solid-phase lubricants are inert powders that create a good slip effect, reducing the rapid thickening of highly viscous melts. They also form vaporization centers, accelerating the overflow of small molecule materials, improving devolatilization efficiency, and reducing the temperature rise effect during melt conveying. This can significantly reduce the kinematic viscosity of highly viscous melts and improve melt conveying efficiency. The addition of solid-phase lubricants creates friction between the fluid surface and the pipe wall, which in turn increases the fluidity of the melt and reduces its viscosity.

[0049] In some embodiments, the preparation method further includes the step of introducing a heat stabilizer, an antioxidant or a colorant into the second esterification kettle before conducting the second esterification reaction; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; and the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

[0050] Introducing heat stabilizers and antioxidants into the second esterification kettle can improve the thermal stability and oxidation resistance of the high-viscosity PET polyester melt, thereby inhibiting the occurrence of side reactions during the esterification and polymerization process, and suppressing the viscosity drop caused by thermal degradation of the high-viscosity melt during the melt direct spinning process of up to 40 to 90 minutes. It also ensures that the intrinsic viscosity level of the melt remains high in the spinning box, thereby producing sufficient elastic curl.

[0051] In some embodiments, the preparation method further includes the step of introducing a liquid lubricant into the high-viscosity PET melt before the high-viscosity PET melt passes through the filter; the liquid lubricant is selected from a combination of one or more of polyethylene glycol with a molecular weight of 8,000 to 20,000, polyetheramine with a molecular weight of 10,000 to 20,000, polybutylene adipate with a molecular weight of 5,000 to 20,000, and polyacrylate.

[0052] Furthermore, the amount of the liquid lubricant is 0.1% to 2.0% of the total mass of the melt, preferably 0.3 to 1.5%, and more preferably 0.5 to 1.0%.

[0053] In some embodiments, the difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 250 to 700 Pa.s, preferably 450 to 630 Pa.s; further preferably, the difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.30 to 0.45, and the difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 500 to 600 Pa.s.

[0054] In some embodiments, the preparation method further comprises the step of mixing the mixture of the solid-phase smoothing agent and the ethylene terephthalate prepolymer through a dynamic mixer before passing the mixture through the filter.

[0055] In some embodiments, the preparation method further comprises the step of filtering the ethylene terephthalate prepolymer in a filter before introducing it into the high-viscosity final polymerization kettle and the low-viscosity final polymerization kettle.

[0056] In some embodiments, the preparation method further comprises the step of passing the high-viscosity PET melt and the low-viscosity PET melt through filters separately before passing them through the same spinning assembly.

[0057] In some embodiments, the high-viscosity final polymerization reactor is disposed on top of the spinning assembly, thereby reducing the conveying distance of the high-viscosity melt synthesized in the high-viscosity final polymerization reactor before spinning.

[0058] In some embodiments, the same spinning assembly is a composite spinning beam.

[0059] In some embodiments, the composite spinning beam includes a composite spinneret.

[0060] The present invention also provides a PET bicomponent elastic fiber prepared by the above preparation method.

[0061] In some embodiments, the curl shrinkage of the PET bicomponent elastic fiber is 18% to 38%.

[0062] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0063] The present invention utilizes a six-reactor polymerization system consisting of a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, a high-viscosity final polymerization reactor, and a low-viscosity final polymerization reactor. The high-viscosity final polymerization reactor is configured as a biaxial stirring system with unequal lengths at the front and rear ends. This configuration allows the low-viscosity zone in the high-viscosity final polymerization reactor to have a length that is unequal to the sum of the lengths of the medium-high-viscosity zone and the high-viscosity zone, thereby lengthening the low-viscosity zone. Furthermore, a special disc reactor configuration and a scraper configuration are provided in the three zones. This significantly increases the viscosity of the high-viscosity melt in the high-viscosity final polymerization reactor and narrows the melt molecular weight distribution. Furthermore, by using the high-viscosity final polymerization reactor and the low-viscosity final polymerization reactor to synthesize the high-viscosity melt and the low-viscosity melt, respectively, the viscosity difference between the high-viscosity melt and the low-viscosity melt can be effectively adjusted, thereby adjusting the curl and shrinkage of the resulting bicomponent elastic fiber.

[0064] Alternatively, the present invention can adopt a double-axis stirring form in which the high-viscosity final polymerization kettle is set to have equal lengths at the front and rear ends, that is, the length of the low-viscosity zone is equal to the sum of the lengths of the medium-high-viscosity zone and the high-viscosity zone, and at the same time, specific disc reactor settings and scraper settings are set in the three zones, which can also achieve the purpose of increasing the viscosity of the high-viscosity melt and effectively adjusting the viscosity difference between the high-viscosity melt and the low-viscosity melt, thereby adjusting the curl rate and shrinkage rate of the final two-component elastic fiber.

[0065] In the present invention, the intrinsic viscosity of the high-viscosity melt can reach 0.68-0.90, and the intrinsic viscosity of the low-viscosity melt is 0.45-0.64. The viscosity of the high-viscosity melt is much higher than that of the prior art.

[0066] The curl shrinkage rate of the PET bicomponent elastic fiber of the present invention can reach 38%, which is much higher than that of the existing bicomponent elastic fiber.

[0067] The preparation method of the present invention is used for industrial production of bicomponent elastic fibers, which can achieve a low-viscosity melt production capacity of 30,000 to 80,000 tons / year and a high-viscosity melt production capacity of 30,000 to 80,000 tons / year. When the product is melt-spun PET / PET high-low viscosity bicomponent elastic fiber, the comprehensive device production capacity is 60,000 to 160,000 tons / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG1 is a schematic diagram of a six-reactor polymerization system used in an embodiment of the present invention;

[0069] FIG2 is a schematic structural diagram of a first high-viscosity polymerization reactor used in an embodiment of the present invention;

[0070] FIG3 is a schematic structural diagram of a second high-viscosity polymerization reactor used in an embodiment of the present invention;

[0071] FIG4 is a schematic structural diagram of a composite scraper used in a final polymerization reactor according to an embodiment of the present invention;

[0072] Among them, 1-low viscosity zone, 2-medium and high viscosity zone, 3-high viscosity zone, 4-composite scraper, 5-disc scraper, 6-axial scraper, 7-wall scraper, 8-stirring shaft, 9-disc reactor, 10-first esterification kettle, 11-second esterification kettle, 12-first prepolymerization kettle, 13-second prepolymerization kettle, 14-high viscosity final polymerization kettle, 15-low viscosity final polymerization kettle, 16-melt pump, 17-steam feed port. DETAILED DESCRIPTION

[0073] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the basic principles, main features, and advantages of the present invention, and the present invention is not limited in scope by the following examples. The implementation conditions used in the examples can be further adjusted according to specific requirements. The implementation conditions not specified are generally those used in routine experiments. Unless otherwise specified in the following examples, all raw materials were purchased commercially or prepared by conventional methods in the art.

[0074] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

[0075] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments of the present invention. In the following embodiments, it should be noted that the terms "front" and "rear" are based on the direction of material flow, with the direction in which the material flows first being the front and the direction in which the material flows later being the rear. For example, in FIG2 , the term "front" refers to the left side of FIG2 , and the term "rear" refers to the right side of FIG2 . Therefore, the directions and positional relationships described in the present invention are merely for the purpose of facilitating the description of the invention and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific direction, only have a specific direction, or be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0076] As shown in Figure 1, in the embodiment, a six-reactor system is used to prepare PET bicomponent elastic fibers: a first esterification reactor 10, a second esterification reactor 11, a first prepolymerization reactor 12, a second prepolymerization reactor 13, a high-viscosity final polymerization reactor 14, and a low-viscosity final polymerization reactor 15. The six reactors are interconnected by necessary pipelines, and are connected to the necessary vacuum systems. A pump 16 and filters A and B are provided between the second prepolymerization reactor 13 and either the high-viscosity final polymerization reactor 14 or the low-viscosity final polymerization reactor 15. In actual production processes, filters A and B are not operated simultaneously. For example, filter A can be operated first, and after the system has been running for a period of time, filter B can be switched to use, at which time filter A can be cleaned.

[0077] For the high viscosity final polymerization kettle 14, the first design is a dual-axis stirring design with unequal lengths at the front and rear ends. As shown in Figure 2, the high viscosity final polymerization kettle 14 includes a main body with a chamber inside, and the main body includes a low viscosity zone 1, a medium-high viscosity zone 2, and a high viscosity zone 3 arranged in sequence along the axial direction of the high viscosity final polymerization kettle 14. The viscosity of the polyethylene terephthalate melt in the low viscosity zone 1, the medium-high viscosity zone 2, and the high viscosity zone 3 increases in sequence. The length of the low viscosity zone 1 is three-fifths of the length of the high viscosity final polymerization kettle 14, and the lengths of the medium-high viscosity zone 2 and the high viscosity zone 3 are two-fifths of the length of the high viscosity final polymerization kettle 14. The high viscosity final polymerization kettle 14 also includes two The stirring shafts 8 are arranged in the low viscosity zone 1, and the other stirring shaft 8 is arranged in the medium and high viscosity zone 2 and the high viscosity zone 3. The central axes of the two stirring shafts 8 are located on the same straight line. The length of the stirring shaft 8 arranged in the low viscosity zone 1 is three-fifths of the length of the high viscosity final polymerization kettle 14, and the length of the stirring shaft 8 arranged in the medium and high viscosity zone 2 and the high viscosity zone 3 is two-fifths of the length of the high viscosity final polymerization kettle 14; the high viscosity final polymerization kettle 14 also includes a trumpet-shaped high viscosity melt outlet arranged at the rear end of the high viscosity zone 3.

[0078] Both stirring shafts 8 are equipped with multiple disc reactors 9. The disc reactors 9 in the low-viscosity zone 1 are designed as a multi-disc assembly of 3 to 10 discs, with a multi-disc assembly of 10 to 6 discs at the front end and a multi-disc assembly of 5 to 3 discs at the rear end. The total number of disc reactors in the low-viscosity zone 1 is 35 to 55. The high-viscosity final polymerization reactor 14 also includes two circular distribution discs at the front end of the low-viscosity zone 1. Each distribution disc has six spokes, dividing the distribution disc into six equal sections. Sieve plates are arranged in three equally spaced sectors, each with a large number of circular holes with a diameter of 1 to 5 cm. The distribution plates control the material flow, preventing short-circuiting of low-viscosity materials and achieving a more uniform molecular weight distribution of the melt.

[0079] The disc reactors 9 in the medium-high viscosity zone 2 are designed with 4 combined discs, 3 combined discs and 2 combined discs from front to back respectively; the medium-high viscosity zone 2 is also provided with a wall scraper 7 for scraping the melt on the inner wall of the high viscosity final polymerization kettle 14; the disc reactors 9 in the medium-high viscosity zone 2 are 15 to 25 discs; the disc reactor 9 in the high viscosity zone 3 is designed with 2 combined discs, and the high viscosity zone 3 is provided with 5 to 8 groups of 2 combined discs; the total number of disc reactors 9 in the medium-high viscosity zone 2 and the high viscosity zone 3 is 25 to 35.

[0080] As shown in Figure 4, the high viscosity area 1 is also provided with a composite scraper 4, which includes an axial scraper 6 for scraping the melt on the stirring shaft, a wall scraper 7 for scraping the melt on the inner wall of the high viscosity final polymerization kettle 14, and a disk scraper 5 for scraping the melt on the stirrer; in the design of the two combined disks in the high viscosity area 3, the distance between the combined disk group and the two disks themselves gradually increases from front to back.

[0081] For the high viscosity final polymerization kettle 14, the second design is a design with equal lengths of the front and rear axes. As shown in FIG3 , the high viscosity final polymerization kettle 14 is a horizontal polymerization kettle and includes a main body with a chamber inside. The main body includes a low viscosity zone 1, a medium-high viscosity zone 2, and a high viscosity zone 3 arranged in sequence along the axial direction of the high viscosity final polymerization kettle 14. The viscosity of the polyethylene terephthalate melt in the low viscosity zone 1, the medium-high viscosity zone 2, and the high viscosity zone 3 increases in sequence. The length of the low viscosity zone 1 is half of the length of the high viscosity final polymerization kettle 14, and the lengths of the medium-high viscosity zone 2 and the high viscosity zone 3 are half of the length of the high viscosity final polymerization kettle 14. The high viscosity final polymerization kettle 14 also has a plurality of axial sections. It includes two stirring shafts 8, one of which is arranged in the low viscosity zone 1, and the other stirring shaft 8 is arranged in the medium and high viscosity zone 2 and the high viscosity zone 3. The central axes of the two stirring shafts 8 are located on the same straight line. The length of the stirring shaft 8 arranged in the low viscosity zone 1 is half of the length of the high viscosity final polymerization kettle 14, and the length of the stirring shaft 8 arranged in the medium and high viscosity zone 2 and the high viscosity zone 3 is half of the length of the high viscosity final polymerization kettle 14; the high viscosity final polymerization kettle 14 also includes a trumpet-shaped high viscosity melt outlet arranged at the rear end of the high viscosity zone 3.

[0082] Multiple disc reactors 9 are provided on both stirring shafts 8; the disc reactor 9 in the low viscosity zone 1 is designed with multiple groups of multiple discs; the high viscosity final polymerization reactor 14 also includes two circular distribution discs arranged at the front end of the low viscosity zone 1, each distribution disc has six spokes, dividing the distribution disc into six equal parts, wherein sieve plates are arranged in three equally divided fan-shaped areas at intervals, and each sieve plate is distributed with a large number of circular holes with a diameter of 1-5 cm.

[0083] The disc reactor 9 in the medium and high viscosity area 2 is designed with 8 to 10 groups of double discs; the disc reactor 9 in the high viscosity area 3 is designed with a single disc, and the disc reactor 9 in the high viscosity area 3 has 6 to 15 discs; the disc reactor 9 in the high viscosity area 3 adopts a reinforced design.

[0084] As shown in Figure 4, the high viscosity zone 3 is also provided with a composite scraper 4, which includes an axial scraper 6 for scraping the melt on the stirring shaft 8, a wall scraper 7 for scraping the melt on the inner wall of the high viscosity final polymerization kettle 14, and a disk scraper 5 for scraping the melt on the stirrer. The wall scraper 7 is a spiral that rotates along the axial direction. The axial scraper 6 and the disk scraper 5 are arranged between the disc reactors 9, and the wall scraper 7 is arranged at the outer edge of the disc reactor 9. From front to back, the distance between the disk scraper 5 and the adjacent disc reactor 9, and the distance between the wall scraper 7 and the inner wall of the high viscosity final polymerization kettle 14 gradually decrease; the diameter of the disc reactor 9 in the high viscosity zone 3 decreases from front to back, and the diameter of the last disc reactor 9 in the high viscosity zone 3 is 85% of the diameter of the first disc reactor 9.

[0085] The high viscosity final polymerization reactor 14 further includes steam feed ports 17 for introducing superheated ethylene glycol steam, which are arranged at the top of the main body at the rear end of the low viscosity zone 1, the rear end of the medium and high viscosity zone 2 and the rear end of the high viscosity zone 3.

[0086] The high viscosity final polymerization reactor 14 is connected to a vacuum pump, which is a liquid ring pump with a chilled water device for cooling the gas at its inlet. The melt pump transports the high viscosity PET melt and the low viscosity PET melt, and a melt cooler is provided at the melt pump outlet.

[0087] A dynamic mixer and a filter are arranged after the second prepolymerization kettle and before the high-viscosity final polymerization kettle; and a solid phase smoothing agent injection system is arranged before the dynamic mixer.

[0088] A dynamic mixer and a filter are arranged after the high-viscosity final polymerization kettle and the low-viscosity final polymerization kettle and before the same spinning assembly; and a viscosity reducing agent injection system is arranged before the dynamic mixer.

[0089] Necessary melt pumps, vacuum pumps and conveying pipelines can be installed on the pipelines connecting the six kettles.

[0090] The same spinning assembly is a composite spinning manifold, and the high-viscosity final polymerization reactor is set on the top of the composite spinning manifold to shorten the conveying distance of the melt, especially the high-viscosity melt. The composite spinning manifold contains a spinneret.

[0091] Example 1

[0092] This embodiment provides a method for preparing a PET bicomponent elastic fiber, and the specific steps are as follows:

[0093] The preparation method of the catalyst used in this embodiment is as follows:

[0094] Sulfuric acid and barium hydroxide or barium acetate are reacted in anhydrous ethylene glycol to prepare an ethylene glycol suspension of barium sulfate nanoparticles, and the generated acetic acid is removed by vacuum purification (when barium acetate is used as the raw material). The particle size of the barium sulfate nanoparticles is 20 to 50 nm, and the specific surface area is 270 to 350 m 2 / g. The pH value of an ethylene glycol suspension of barium sulfate nanoparticles is adjusted to 7.0-7.1. Then, a mixed aqueous solution of scandium sulfate, magnesium sulfate, cobalt sulfate, and zinc sulfate, and an ethylene glycol solution of sodium hydroxide are simultaneously added dropwise to the ethylene glycol suspension under high-speed stirring. After the addition is complete, the suspension is aged for 8.0 hours. Then, a titanium compound, tetrabutyl titanate or isopropyl titanate, is added dropwise to the aged suspension over 5.0 hours. Aging is continued for 6.0 hours. Finally, a silane coupling agent is added dropwise to the suspension to seal the powder surface. After aging for another 10.0 hours, water and low-boiling alcohol are distilled off, and the pH of the suspension is adjusted to neutral. After filtration, the product is placed in a muffle furnace and heat-set at 480-525°C to obtain a supported catalyst. The catalyst uses barium sulfate nanoparticles as a carrier and scandium oxide, magnesium oxide, cobalt oxide, zinc oxide, and titanium oxide as active components. The catalyst contains 3.3% to 10.0% titanium oxide and oxides of scandium, magnesium, cobalt and zinc as auxiliary active ingredients, the content of the auxiliary oxides accounts for 8% to 15% of the total solid phase of the catalyst, and the amount of the barium sulfate carrier accounts for 75.0% to 88.7% of the total solid phase.

[0095] The above-mentioned six-reactor polymerization device is used to sequentially pass terephthalic acid, ethylene glycol, and the above-mentioned catalyst through the first esterification reactor and the second esterification reactor for esterification reaction, and the first prepolymerization reactor and the second prepolymerization reactor for prepolymerization reaction to obtain ethylene terephthalate prepolymer. Before the second esterification reaction in the second esterification reactor, ordinary titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, wherein titanium dioxide accounts for 10wt% and ethylene glycol accounts for 90wt%), heat stabilizer, antioxidant, colorant are passed through corresponding pipes. The terephthalate prepolymer is fed into different chambers of a second esterification reactor, wherein the flow rate of terephthalic acid is 2,500 to 25,000 kg / h, and the flow rate of ethylene glycol is 1,000 to 10,000 kg / h. The catalyst is used in an amount such that the titanium element accounts for 8 to 12 ppm of the total mass of the melt. The matting agent is used in an amount such that titanium dioxide accounts for 0.3% of the total mass of the melt. The heat stabilizer, antioxidant, and colorant are added in amounts of 20 ppm, 50 ppm, and 1 ppm, respectively, relative to the molar amount of terephthalic acid. The ethylene terephthalate prepolymer is then fed into a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor for polymerization, respectively, to produce a high-viscosity PET melt and a low-viscosity PET melt. Finally, the high-viscosity PET melt and the low-viscosity PET melt are directly fed into the same parallel composite spinning beam at a mass ratio of 5:5 for spinning to produce a PET bicomponent elastic fiber.

[0096] Example 1 Group experiments include 1-1, 1-2 to 9-1, 9-2, and their data are shown in Table 1 below:

[0097] The conditions set up for the six-reactor polymerization unit and the properties of the high-viscosity PET melt and the low-viscosity PET melt are shown in Table 1. The intrinsic viscosity is measured by dissolving the melt in a mixed solvent of phenol and tetrachloroethane (3:2 by volume), and the unit is dL / g.

[0098] Table 1 Process conditions and viscosity of Example 1

[0099] The high-viscosity PET melt and the low-viscosity PET melt corresponding to Example 1 were transported to the spinneret. The melt index and viscosity difference during spinning into fibers are shown in Table 2 below. The fiber properties of the present invention were tested in accordance with the GBT 8960-2015 test standard:

[0100] Table 2 Process conditions and viscosity at the spinning manifold of Example 1

[0101] The properties of the composite elastic fibers obtained by spinning the high-viscosity PET melt and the low-viscosity PET melt corresponding to Example 1 are shown in Table 3:

[0102] Table 3 Physical and chemical indicators of PET / PET two-component composite elastic fiber of Example 1

[0103] Example 2

[0104] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 1, differing only in that a solid-phase smoothing agent is also introduced from the solid-phase smoothing agent injection system. Specifically, the solid-phase smoothing agent is a polyester masterbatch of talc with a particle size of 100-250 nm, and the amount used is 0.25% relative to the total mass of the melt. The different intrinsic viscosities of the high-viscosity melt and the low-viscosity melt are controlled to be within a range of 0.80-0.90. The corresponding apparatus conditions and melt properties are shown in Table 4 below. The high-viscosity melt and the low-viscosity melt are conveyed to the spinneret, and the melt indices and viscosity differences during spinning are shown in Table 5 below. Sequence numbers 10-1, 10-2, and 10-3 correspond to Example 2.

[0105] Example 3

[0106] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 1, differing only in that a viscosity reducer is also introduced from the viscosity reducer injection system. The specific type is PETG polyester with an intrinsic viscosity of 0.58 (the intrinsic viscosity is measured using phenol:tetrachloroethane (3:2 volume ratio)), and the amount used is 0.5% relative to the total mass of the melt. The different intrinsic viscosities of the high-viscosity melt and the low-viscosity melt are controlled to maintain the intrinsic viscosity of the high-viscosity melt within a range of 0.80 to 0.90. The corresponding apparatus conditions and melt properties are shown in Table 4 below. The high-viscosity melt and the low-viscosity melt are transported to the spinneret, and the melt indices and viscosity differences during spinning into fibers are shown in Table 5 below. Sequence numbers 11-1, 11-2, and 11-3 correspond to Example 3.

[0107] Example 4

[0108] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 1, differing only in that a liquid lubricant is also introduced from a liquid lubricant injection system. Specifically, the lubricant is polybutylene adipate with a molecular weight of 10,000, and the amount used is 0.25% relative to the total mass of the melt. The different intrinsic viscosities of the high-viscosity melt and the low-viscosity melt are controlled to be within a range of 0.80 to 0.90. The corresponding apparatus conditions and melt properties are shown in Table 4 below. The high-viscosity melt and the low-viscosity melt are conveyed to the spinneret, and the melt indices and viscosity differences during spinning are shown in Table 5 below. Sequence numbers 12-1, 12-2, and 12-3 correspond to Example 4.

[0109] Table 4 Process conditions and viscosity of Examples 2-4

[0110] Table 5 Process conditions and viscosity of spinning manifold in Examples 2-4

[0111] The properties of the composite elastic fibers obtained by spinning the high-viscosity PET melt and the low-viscosity PET melt corresponding to Example 2-4 are shown in Table 6, where the fiber variety is FDY:

[0112] Table 6 Physical and chemical indicators of two-component composite elastic fibers of Examples 2-4

[0113] Comparing the results of Examples 2-4 with those of Example 1, it can be seen that due to the degradation reaction of the high-viscosity PET melt during transportation, the viscosity of the high-viscosity melt at the spinning manifold becomes lower, and the actual viscosity difference between the high-viscosity and low-viscosity melts at the spinning manifold is lower than the viscosity difference between the two melt slices. After a solid-phase smoothing agent, a viscosity reducer or a liquid-phase lubricant is introduced into the polymerization system, the viscosity drop of the high-viscosity melt during melt transportation will be significantly suppressed, and the pipeline transportation temperature will be significantly reduced, thereby improving the spinning conditions and increasing the full roll rate of the fiber product.

[0114] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications based on the spirit and essence of the present invention are intended to be encompassed by the scope of protection of the present invention.

Claims

1. A method for preparing a PET two-component elastic fiber, comprising the steps of subjecting terephthalic acid, ethylene glycol and a catalyst to an esterification reaction in a first esterification kettle and a second esterification kettle, and a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain an ethylene terephthalate prepolymer, wherein: The preparation method also includes the steps of conveying the ethylene terephthalate prepolymer to a high-viscosity final polymerization kettle and a low-viscosity final polymerization kettle respectively through separate melt pumps for polymerization reaction to obtain a high-viscosity PET melt and a low-viscosity PET melt respectively, wherein the viscosity of the high-viscosity PET melt is greater than the viscosity of the low-viscosity PET melt; and spinning the high-viscosity PET melt and the low-viscosity PET melt through the same parallel composite spinning assembly to obtain the PET two-component elastic fiber; the difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.100-0.

550.

2. The preparation method according to claim 1, characterized in that: The high viscosity final polymerization kettle is a horizontal polymerization kettle, and includes a main body with a chamber inside, the main body includes a low viscosity zone, a medium-high viscosity zone, and a high viscosity zone arranged in sequence along the axial direction of the high viscosity final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low viscosity zone, the medium-high viscosity zone, and the high viscosity zone increases in sequence, the length of the low viscosity zone is three-fifths of the length of the high viscosity final polymerization kettle, the lengths of the medium-high viscosity zone and the high viscosity zone are two-fifths of the length of the final polymerization kettle, the high viscosity final polymerization kettle also includes two stirring shafts, one of which is arranged in the low viscosity zone, and the other is arranged in the medium-high viscosity zone and the high viscosity zone, the central axes of the two stirring shafts are located on the same straight line, the length of the stirring shaft arranged in the low viscosity zone is three-fifths of the length of the high viscosity final polymerization kettle, and the lengths of the stirring shafts arranged in the medium-high viscosity zone and the high viscosity zone are two-fifths of the length of the high viscosity final polymerization kettle; the high viscosity final polymerization kettle also includes a trumpet-shaped high viscosity melt outlet arranged at the rear end of the high viscosity zone.

3. The preparation method according to claim 2, characterized in that: A plurality of disc reactors are arranged on the two stirring shafts; the disc reactor in the low viscosity zone is designed as a multi-disc group of 3 to 10 discs, the front end of the low viscosity zone is designed as a multi-disc group of 10 to 6 discs, the rear end of the low viscosity zone is designed as a multi-disc group of 5 to 3 discs, and the disc reactor in the low viscosity zone is 35 to 55 discs; the high viscosity final polymerization kettle also includes two circular distribution discs arranged at the front end of the low viscosity zone, each distribution disc has six spokes, and the distribution disc is divided into six equal parts, wherein sieve plates are arranged in three equally divided fan-shaped areas distributed at intervals, and a large number of circular holes with a diameter of 1-5 cm are distributed on each sieve plate.

4. The preparation method according to claim 3, characterized in that: The disc reactor in the medium and high viscosity zone is designed with 4 combined discs, 3 combined discs and 2 combined discs from front to back respectively; the medium and high viscosity zone is also provided with a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle; the disc reactor in the medium and high viscosity zone is 15 to 25 discs; the disc reactor in the high viscosity zone is designed with 2 combined discs, and the high viscosity zone is provided with 5 to 8 groups of 2 combined discs; the total number of disc reactors in the medium and high viscosity zone and the high viscosity zone is 25 to 35; the high viscosity zone is also provided with a composite scraper, and the composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle and a disc scraper for scraping the melt on the stirrer; in the 2-piece combined disc design of the high viscosity zone, the distance between the combined disc groups and between the two discs themselves gradually increases from front to back.

5. The preparation method according to claim 3, characterized in that: The intrinsic viscosity of the polyethylene terephthalate melt in the low-viscosity zone is 0.45-0.60, and the dynamic viscosity is 90-240 Pa.s; the intrinsic viscosity of the polyethylene terephthalate melt in the high-viscosity zone is 0.68-0.90, and the dynamic viscosity is 500-1000 Pa.s.

6. The preparation method according to claim 1, characterized in that: The high viscosity final polymerization kettle is a horizontal polymerization kettle, and includes a main body with a chamber inside, the main body includes a low viscosity zone, a medium-high viscosity zone, and a high viscosity zone arranged in sequence along the axial direction of the high viscosity final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low viscosity zone, the medium-high viscosity zone, and the high viscosity zone increases in sequence, the length of the low viscosity zone is half of the length of the high viscosity final polymerization kettle, the lengths of the medium-high viscosity zone and the high viscosity zone are half of the length of the high viscosity final polymerization kettle, the high viscosity final polymerization kettle also includes two stirring shafts, one of which is arranged in the low viscosity zone, and the other stirring shaft is arranged in the medium-high viscosity zone and the high viscosity zone, the central axes of the two stirring shafts are located on the same straight line, the length of the stirring shaft arranged in the low viscosity zone is half of the length of the high viscosity final polymerization kettle, and the lengths of the stirring shafts arranged in the medium-high viscosity zone and the high viscosity zone are half of the length of the high viscosity final polymerization kettle; the high viscosity final polymerization kettle also includes a trumpet-shaped high viscosity melt outlet arranged at the rear end of the high viscosity zone.

7. The preparation method according to claim 6, characterized in that: A plurality of disc reactors are arranged on the two stirring shafts; the disc reactor in the low viscosity zone is designed with multiple groups of multiple discs; the high viscosity final polymerization kettle also includes two circular distribution plates arranged at the front end of the low viscosity zone, each distribution plate has six spokes, and the distribution plate is divided into six equal parts, wherein sieve plates are arranged in three equally divided fan-shaped areas distributed at intervals, and a large number of circular holes with a diameter of 1-5 cm are distributed on each sieve plate.

8. The preparation method according to claim 6, characterized in that: The disc reactor in the medium and high viscosity zone is designed with 8 to 10 groups of double discs; the disc reactor in the high viscosity zone is designed with a single disc, and the disc reactor in the high viscosity zone is 6 to 15 discs; the disc reactor in the high viscosity zone adopts a reinforced design; the high viscosity zone is also provided with a composite scraper, the composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high viscosity final polymerization kettle, and a disc scraper for scraping the melt on the stirrer, the wall scraper is a spiral that rotates along the axial direction, the axial scraper and the disc scraper are arranged between the disc reactors, and the wall scraper is arranged at the outer edge of the disc reactor, and from front to back, the distance between the disc scraper and the adjacent disc reactor, and the distance between the wall scraper and the inner wall of the high viscosity final polymerization kettle gradually decrease; the diameter of the disc reactor in the high viscosity zone decreases from front to back, and the diameter of the last disc reactor in the high viscosity zone is 85% of the diameter of the first disc reactor.

9. The preparation method according to claim 6, characterized in that: The intrinsic viscosity of the polyethylene terephthalate melt in the low-viscosity region is 0.45-0.60, and the dynamic viscosity is 90-240 Pa.s; the intrinsic viscosity of the polyethylene terephthalate melt in the high-viscosity region is 0.68-0.90, and the dynamic viscosity is 450-1000 Pa.s.

10. The preparation method according to claim 2 or 6, characterized in that: The high viscosity final polymerization kettle also includes steam feed ports for introducing superheated ethylene glycol steam, which are arranged at the top of the main body at the rear end of the low viscosity zone, the rear end of the medium and high viscosity zone, and the rear end of the high viscosity zone. The preparation method also includes the step of using a metering system to meter the superheated ethylene glycol steam and introducing it into the high viscosity final polymerization kettle.

11. The preparation method according to claim 2 or 6, characterized in that: The high viscosity final polymerization kettle is connected to a vacuum pump, which is a liquid ring pump, and a chilled water device for cooling the gas is provided at its inlet. The preparation method controls the suction volume of the vacuum pump to 200-350 kg / h and controls the vacuum degree in the high viscosity final polymerization kettle to 100-180 Pa.

12. The preparation method according to claim 2 or 6, characterized in that: The catalyst is a supported catalyst and includes a carrier and an active component; the carrier is nano-barium sulfate, the particle size of the nano-barium sulfate is 20-50 nm, and the specific surface area is 270-350 m 2 / g; the nano barium sulfate is prepared by reaction in anhydrous ethylene glycol; the active components include a main active component and a secondary active component, the main active component is titanium oxide, and the secondary active component is a mixture of scandium oxide, magnesium oxide, cobalt oxide and zinc oxide.

13. The preparation method according to claim 12, characterized in that: According to weight percentage, the catalyst contains 3.3% to 10.0% of titanium oxide, 8% to 15% of secondary active components, and 75.0% to 88.7% of nano-barium sulfate; and / or, the particle size of the catalyst is 80 to 160nm; and / or, the catalyst is prepared by precipitating a carrier ethylene glycol suspension, scandium sulfate, magnesium sulfate, cobalt sulfate, zinc sulfate, a titanium compound and a precipitant, treating the surface with a silane coupling agent, and calcining.

14. The preparation method according to claim 2 or 6, characterized in that: A melt pump is used to transport high-viscosity PET melt and low-viscosity PET melt, a melt cooler is arranged at the outlet of the melt pump, and the preparation method controls the temperature of the high-viscosity PET melt to be 284-286°C after being cooled by the melt cooler; a filter and a booster pump are arranged between the melt pump and the parallel composite spinning component; the preparation method controls the transportation time of the high-viscosity PET melt to be 25-35 minutes; and a plurality of static slow-flow mixers are arranged at the front end of the melt transportation pipeline.

15. The preparation method according to claim 14, characterized in that: The preparation method also includes the step of introducing a viscosity reducer into the high-viscosity PET melt before the high-viscosity PET melt passes through a filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, normal pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, and polypropylene terephthalate-1,3-glycol terephthalate PTT.

16. The preparation method according to claim 2 or 6, characterized in that: The preparation method further comprises the steps of introducing a solid-phase smoothing agent into the ethylene terephthalate prepolymer before the ethylene terephthalate prepolymer is introduced into the high-viscosity final polymerization kettle, and passing a mixture of the solid-phase smoothing agent and the ethylene terephthalate prepolymer through a filter, wherein the solid-phase smoothing agent is in the form of a masterbatch and comprises a polyester matrix and an inorganic powder, wherein the inorganic powder is selected from a combination of one or more of talc, montmorillonite, barium sulfate, hydrotalcite and nano-silica.

17. The preparation method according to claim 2 or 6, characterized in that: The preparation method also includes the step of introducing a heat stabilizer, an antioxidant or a colorant into the second esterification kettle before the second esterification reaction; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

18. The preparation method according to claim 13, characterized in that: The preparation method also includes the step of introducing a liquid lubricant into the high-viscosity PET melt before the high-viscosity PET melt passes through a filter; the liquid lubricant is selected from a combination of one or more of polyethylene glycol with a molecular weight of 8,000 to 20,000, polyetheramine with a molecular weight of 10,000 to 20,000, polybutylene adipate with a molecular weight of 5,000 to 20,000, and polyacrylate.

19. The preparation method according to claim 1, characterized in that: In terms of mass percentage, the PET bicomponent elastic fiber contains 30%-70% of a first PET component and 70%-30% of a second PET component, and the first PET component and the second PET component have different viscosities.

20. The preparation method according to claim 2 or 6, characterized in that: The difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 250-700 Pa.s, preferably 450-630 Pa.s; further preferably, the difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.30-0.45, and the difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 500-600 Pa.s.

21. The PET bicomponent elastic fiber prepared by the preparation method according to any one of claims 1 to 20.

22. The PET bicomponent elastic fiber according to claim 21, characterized in that: The PET bicomponent elastic fiber is POY fiber, and its full roll rate is 90% to 98%; or, the PET bicomponent elastic fiber is FDY fiber, and its full roll rate is 95% to 99%, and the elastic shrinkage rate of the fabric is 20% to 45%; or, the PET bicomponent elastic fiber is DTY fiber, and its full roll rate is 88% to 96%.

23. The PET bicomponent elastic fiber according to claim 22, characterized in that: The curling shrinkage rate of the PET two-component elastic fiber is 18% to 38%.

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